Vent orifice in fluid catalytic cracking direct-connected cyclone apparatus

Abstract: A cyclone roof (12) has an aperture (10) and an outlet tube (22) extends through the aperture. A ring plate member (16) overlies the roof and its opening has a diameter smaller than the diameter of the roof aperture. The opening has an erosion protective covering (18) and defines a ware-resistant annular vent orifice (24) between the protective covering (18) and the outlet tube (22).

Description: The present invention pertains to the formation of a vent orifice in fluid catalytic cracking direct-connected cyclone apparatus. Our published European patent application no. EP-A-0488549, the disclosure of which is incorporated herein by reference, describes an apparatus for rapidly separating catalyst from a cracked hydrocarbon gas in a fluidized catalytic cracking (FCC) unit. It also describes a process for withdrawing stripper gas from an FCC reactor vessel. A feature of the described invention is the location of the vent orifice for reactor and stripper gasses in an annular space formed around the reactor cyclone outlet tube through the roof of the reactor cyclone. This location for the vent orifice has been shown to have a technical advantage over systems practised by others in the operation and pressure balance of direct-connected cyclone systems. In the direct-connected cyclone system the vent orifice may serve as an expansion connection between the first stage reactor cyclone and the second stage or upper cyclone. In this case, freedom of movement between the reactor cyclone outlet tube and cyclone roof must be maintained. Sizing of the vent orifice and maintenance of the vent orifice clearance is critical to maintaining proper operation of the direct-connected cyclone during an extended run on an FCCU. The tolerances required to maintain the proper pressure balance in the system are very small. For example, in one system, the width of the annular gap of the vent orifice is only about 20mm. In some designs it may be necessary to provide for lateral expansion which exceeds the width of the gap between the cyclone outlet tube and cyclone roof. In other words, when the gap is designed for the proper pressure drop, there may not be enough clearance to provide for lateral expansion. The process of fluid catalytic cracking (FCC) comprises mixing hot regenerated catalyst with a hydrocarbon feedstock in a transfer line riser reactor under catalytic cracking reaction conditions. The feedstock is cracked to yield gasoline boiling range hydrocarbon as well as degradation products, such as coke which deposits on the catalyst causing a reduction in catalytic activity. Hydrocarbon vapor and coked catalyst are passed from the top of the riser reactor directly to a separator vessel, typically a cyclone separator, wherein catalyst is separated from hydrocarbon. In the FCC art, the separator vessel is termed the reactor vessel. The separated catalyst is passed to a stripper wherein it is contacted with a stripping gas to remove volatile hydrocarbon. Stripped catalyst is then passed to a separate regeneration vessel wherein coke is removed from the catalyst by oxidation at a controlled rate. Catalyst, substantially freed of coke, is collected in a vertically oriented regenerated catalyst standpipe. The catalyst is passed from the standpipe to the riser reactor for cyclic reuse in the process. U.S. patents 4,623,446 and 4,737,346 to J. H. Haddad et al teach a closed coupled cyclone separator system in the reactor vessel of a fluid catalytic cracking apparatus. Means is provided for blending stripping gas with cracked hydrocarbon as it flows to a directly coupled riser cyclone separator. As shown in Fig. 7 and 8, the riser reactor conduit is modified to comprise an overlapping downstream portion 118 to provide an annulus between the upstream portion 117 and the downstream portion 118. The annulus is covered by a flat metal ring having orifices 125 in open communication with the reactor vessel, enabling stripping gas to pass into the downstream conduit 118. A riser cyclone dipleg is sized, as seen in Fig. 5, to admit at least a portion of stripping gas from the stripping zone to pass countercurrent to catalyst passing downwardly through the dipleg. U.S. Patent 4,502,947 to Haddad et al discloses a closed cyclone fluid catalytic cracking catalyst separation method and apparatus. In the closed cyclone, hydrocarbon product and catalyst are passed directly into a cyclone separator from a riser without passing into the atmosphere of the reactor vessel. Avoiding the atmosphere of the reactor vessel reduces both excess catalytic cracking and high temperature thermal cracking. The present invention concerns constructing and attaching vent orifice forming means in a direct-connected cyclone system. The proposed vent orifice forming means will maintain free movement between the cyclone outlet tube and cyclone roof even when the lateral expansion requirements exceed the available orifice width. The low wear vent orifice, according to the present invention, is formed by an aperture in the roof of a cyclone, an annular plate of larger outer diameter than the aperture overlying the aperture, erosion protection means covering at least the inner annulus of the annular plate, and an outlet tube mounted passing through the inner annulus defining the vent orifice therebetween. The present invention will now be described, by way of example, with reference to the accompanying drawing in which the single Figure is a vertical section through a portion of a direct-connected cyclone system incorporating the present invention. The subject vent orifice forming means will allow an annular gap between a cyclone roof and an outlet tube to be made to tight tolerances from materials that will resist the erosive action of the entering dust laden vapors. The present invention can also provide for lateral and vertical movement between the outlet tube and cyclone roof which movement exceeds the width of the gap. As shown in the single Figure an opening 10 is formed in a cyclone roof 12 having an inner erosion resistant lining 14. The opening 10 is made larger than the required vent orifice diameter by several inches or more. A ring plate 16 is dimensioned so as to overlap the opening 10 in the cyclone roof 12. A refractory lining 18 with appropriate anchoring system (i.e., hexmesh, s-bar, wavy V anchors, etc.) or, as an alternative, an appropriate erosion resistant ceramic material, is applied to the ring plate 16 to protect those areas of the vent orifice directly exposed to the vapors and catalyst flowing at high velocity. The refractory or ceramic lining can then be cured according to the manufacturer's recommendations prior to finish grinding to the close tolerances required. A cyclone outlet tube 22, which forms the inner wall of the vent orifice annulus 24, is also shop fabricated and refractory or ceramic lined 26. After the refractory or ceramic is properly cured, the outer surface of the outlet tube, in the area which forms the vent orifice, is finish ground to achieve the proper tolerance. The outlet tube can later be field welded to an inlet duct (not shown) of the upper cyclone (also not shown). Three methods are suggested for attachment of the ring plate 16 to the cyclone roof 12. In applications where there is only a small lateral expansion, the ring plate can be attached with a seal weld around the entire outer circumference of the ring plate. If the lateral movement from expansion is greater than can be accommodated by the width of the vent orifice, the plate can be bolted to the cyclone roof with slotted bolt openings in the ring plate providing for additional movement of the plate. A third method is to have the ring plate unconnected to the cyclone roof. In this free floating arrangement the surfaces of the plate and cyclone roof are machined to a smooth finish to provide a good metal-to-metal seal. The pressure drop across the vent orifice will hold the plate in contact with the cyclone roof while still allowing the lateral movement of the plate. The present invention provides the following specific advantages: 1. it allows shop fabrication and repair of the vent orifice without major field work on the cyclone bodies; 2. it allows the vent orifice to be constructed from materials which will resist the erosion of the high velocity gas and catalyst stream; 3. it allows tight tolerances to be maintained on the vent orifice surfaces; 4. it allows for large differential movement of the first and second stage direct-connected cyclones; 5. it allows cyclones to be installed without need of large expansion joints in the outlet tubes or other parts of the riser/cyclone system; and 6. it prevents deformation of the cyclone body due to differential thermal expansion. The present invention may be subject to many modifications and changes without departing from the essential characteristics thereof. The present embodiment is therefor intended in all respects to be illustrative and not restrictive of the scope of the invention.

Claims: A direct-connected cyclone system having an annular vent orifice (24), comprising a cyclone having a roof (12) characterized by: an annular plate member (16) overlying the roof and whose opening has a circumferential wall surface with a diameter smaller than the diameter of a roof aperture (10); an erosion protection covering (18) disposed on and adjacent to at least said circumferential wall surface of said opening of the annular plate member (16) and being disposed towards the roof (12) so as to define the aperture (10); and a cyclone outlet tube (22) extending through said opening of said annular plate member (16) and spaced therefrom to define the annular vent orifice (24) therebetween. A cyclone system according to Claim 1 characterized in that said cyclone outlet tube (22) is externally coated with a refractory material (26). A cyclone system according to Claim 2 characterized in that said refractory material (26) is polished in the area adjacent said vent orifice (24). A cyclone system according to any one of Claims 1 to 3 characterized in that said erosion protection covering (18) comprises a ceramic material. A cyclone system according to any one of Claims 1 to 3 characterized in that said erosion protection covering (18) comprises a refractory material. A cyclone system according to any one of Claims 1 to 5 characterized by means fixedly securing said annular plate member (16) to said roof (12). A cyclone system according to any one of Claims 1 to 5 characterized by means securing said annular plate member (16) to said roof (12) allowing relative movement therebetween.

Inventors: CASTAGNOS JR LEONCE FRANCIS, COLLIER GARY EDMUND, KEINER STEVEN LOUIS, CASTAGNOS, JR., LEONCE FRANCIS, COLLIER, GARY EDMUND, KEINER, STEVEN LOUIS
Applicants: ABB LUMMUS GLOBAL INC, ABB LUMMUS GLOBAL INC.
Application year: 1994
Main classification: C10G11
IPC codes: C10G11, B04C5, B01J8